1. Field of the Invention
The present invention relates to flat panel display devices and, more particularly, to organic light emitting devices and methods of fabricating the same having cathode electrodes to prevent oxygen and/or moisture from infiltrating.
2. Description of the Related Art
An organic light emitting device is a flat panel display device that is an emissive display device in which an organic compound is electrically excited to emit light. The organic compound has characteristics such as a low driving voltage and a thin type. Moreover, since the organic light emitting device has features such as a wide viewing angle, quick response time, and the like, which are required in a liquid crystal display that is a flat panel display device, the organic light emitting device has attracted attention as a next generation display device.
For the organic light emitting device, a problem has arisen as to a life span of a device depending on a passivation method. To solve this problem, Japanese patent publication No. 4-334895, for example, discloses a dual passivation method for a long life span of the display device.
FIG. 1 shows a cross-sectional structure of a flat panel display device made with the conventional dual passivation method. Referring to FIG. 1, in the conventional organic light emitting device, an organic light emitting (hereinafter, referred to as “organic EL”) element 20 has an anode electrode 21, an organic thin film layer 22, and a cathode electrode 23, which are laminated on a glass substrate 10. An inorganic encapsulating layer 30 is formed to cover the organic EL element 20, and the organic EL element 20 and the inorganic encapsulating layer 30 are encapsulated with an encapsulating substrate 50. Here, the encapsulating substrate 50 encapsulates by using an adhesive resin layer 40 such as a light-curing adhesive with a low moisture absorption property in order to prevent moisture infiltration.
The conventional display device used the inorganic encapsulating layer 30 to passivate the organic EL element 20. The inorganic encapsulating layer 30 was formed by using a Chemical Vapor Deposition (CVD) method or a Physical Vapor Deposition (PVD) method, where an organic thin film that is an underlying layer is susceptible to heat and mechanical stresses. As such, the inorganic encapsulating layer 30 does not have a good film quality. Moreover, the inorganic encapsulating layer 30 has a porous structural property so that the inorganic encapsulating layer 30 is susceptible to moisture infiltration. Thus, a perfect passivation could not be performed. Therefore, in the conventional art, the life span of the device cannot be guaranteed only with the inorganic encapsulating layer 30, so that there was a problem that a second passivation must be performed with the adhesive resin and the encapsulating substrate.